This invention relates to phosphorus fertilizers and in particular to a fertilizer having a combination of phosphorous acid or its salts thereof, and either (a) polyphosphoric acid and its salts thereof; or (b) phosphoric acid and its salts thereof. This combination phosphorus fertilizer, when combined within a specific ratio range, increases the phosphorus uptake to plants which enhances plant growth.
Fertilizers have long been used to supply needed nutrition to plants. The principal components of plant fertilizers have centered on three elements: nitrogen, phosphorus and potassium.
Phosphorus is not found in nature in its elemental form. The principal source of phosphorus for the fertilizer industry is obtained from the ores of phosphorus-containing minerals. The usual practice in the fertilizer industry is to convert phosphorus ores into a phosphorus product containing the phosphoric radical (PO.sub.4.sup.-3) which can be absorbed, although rather inefficiently, into plants and thereafter used as nutrition. It is well known in the prior art that phosphorus is biologically active and nutritionally useful to plants only in the phosphoric form (PO.sub.4.sup.-3). A common source of the phosphoric radical (PO.sub.4.sup.-3) for fertilizers is phosphoric acid.
Many of the phosphorus fertilizers currently used have a number of undesired qualities. First, if prepared in concentrated solutions, they must be used rather quickly; otherwise, the concentrated solution tends to form undesired precipitates. Further, they must be maintained within a narrow pH range to prevent precipitation, which results in fertilizers with limited application. Precipitates are undesirable since they cannot be absorbed by plants.
Still another problem with phosphorus containing fertilizers, particularly phosphoric fertilizers, is that they are not readily absorbed by foliage and must be applied to the soil and thereafter absorbed by the plant root system. Since only a small portion of the phosphoric fertilizer applied to the soil is actually absorbed by a root system, frequent reapplication usually occurs. This is undesirable because it can lead to leaching of phosphate into the groundwater which may cause eutrophication of lakes, ponds and streams.
Prior art formulas of phosphorus fertilizers have identified these problems. U.S. Pat. No. 5,514,200, issued to Lovatt, describes a formula utilizing the more readily absorbed phosphorous form (PO.sub.3.sup.-3) in a composition buffered with an organic acid. However, as is discussed below, the present invention represents an improved and more effective composition for providing phosphorus to plants.